Research On The Method And Effect Of Deep Foundation Pit Support For Subway Station

With the rise of subway,urban high buildings,as well as the construction of underground space engineering,foundation pit engineering gradually becomes the focus of civil engineering.However,regarding the situations about being close to underground construction such as underground structure,subway station and so on,the back of the supporting structure of soil failure surface will be subject to the conditions of underground structures,and the earth pressure distribution form is different from general situation,causing the general difference between the deformation and internal force of support structure,but at present the study of such problems are relatively few.On the basis of previous studies,taking the deep foundation pit of a subway station in Xi'an city as the background,and with the application of large general finite element software ABAQUS,considering the formation site condition and the subway station structure and foundation pit supporting system,we establish a three-dimensional finite element model,carrying on the dynamic simulation to the hole excavated for building foundation construction actual process,and discuss about the limit of the width of the range of soil deformation of deep foundation pit supporting structure traits,and the results showed that:(1)The existence of the subway station has a "block" effect.on foundation pit deformation.Near the subway station near the maximum lateral displacement of foundation pit retaining structure side without the station is small,and with the decrease of the distance between the subway station and the foundation pit,the "block" effect becomes increasingly significant with the increase of excavation depth,excavation depth "block" effects in metro station and is negatively correlated with the distance between them.(2)For single row of cantilever pile,this paper puts forward the basis of the reasonable value of each design factor,which is based on the efficiency factor of pile length,the efficiency of pile diameter,and the efficiency coefficient of pile spacing.The results show that when the pile length is about 1.8 times the excavation depth can achieve good supporting effect,with theincrease of the pile length,the lateral displacement of the retaining structure decreases gradually,and the pile length efficiency coefficient also decreases gradually and efficiency coefficient of the pile with pile length increased linearly decreases.With the increase of the diameter of the pile,the efficiency coefficient of the pile diameter decreases gradually,and the relationship between the pile diameter and the pile diameter decreases gradually.With the decrease of the spacing between the piles,the efficiency coefficient of spacing increases gradually.(3)Compared with single row cantilever piles,the bottom anchor single row piles can enhance the support performance of the support structure,the angle of the anchor bolt is smaller,and the effect of the support structure is better.When using the single row type anchor rod,the arrangement position of anchor is closer to the top of supporting structure,and when a support structure of the lateral deformation is small,the similar is the two rows of bolt and a bolt row.When laying distance within a reasonable range,the arrangement position of the first row of bolt is of great importance to the role,and two rows of bolt are close to a support structure at the top of the combination produced the deformation can be reduced to the minimum.The length of anchor rod extends out of the sliding surface to limit the deformation of retaining structure.And with the increase of the length of anchor,supporting structure of the lateral deformation gradually decreased,but the decreasing level is gradually reduced,and the length of anchor to support retaining structure deformation controlling role gradually decreases with increasing the length of rock bolt.(4)In the complicated surroundings around foundation pit,double row piles supporting structure has good adaptability,effectively control the pit lateral deformation,reducing the foundation pit excavation on the surrounding environment.(5)The door type rigid frame of double-row piles supporting structure system deformation properties are greatly influenced by the row spacing,pile diameter,pile length minimal impact.Increasing the row spacing can enhance the supporting effect of the supporting structure,and in front of the pile the sensitivity is greater than the back row pile row distance change.Front and back row pile length design is reasonable.the back row pile length change of the influence of the lateral deformation of the retaining structure is relatively small,and the back pile length decreases in a certain range can improve the supporting structure of supporting performance;Lateral displacement of retaining structure in front of the pile length change is more sensitive,and the increase of the front pile long reduces the lateral displacement of the structure,so this should not be adopted in the design of situation that the back pile length is larger than the front pile.